#define _CRT_SECURE_NO_WARNINGS
class Solution {
public:
    vector<int> tmp;
    int reversePairs(vector<int>& nums) {
        tmp.resize(nums.size());
        return MergeSort(nums, 0, nums.size() - 1);
    }
    int MergeSort(vector<int>& nums, int left, int right)
    {
        if (left >= right) return 0;
        int mid = (right - left) / 2 + left;
        int ret = 0;
        ret += MergeSort(nums, left, mid);
        ret += MergeSort(nums, mid + 1, right);
        int cur1 = left, cur2 = mid + 1, i = 0;
        while (cur1 <= mid && cur2 <= right)
        {
            if (nums[cur1] <= nums[cur2])
            {
                tmp[i++] = nums[cur2++];
            }
            else
            {
                ret += right - cur2 + 1;
                tmp[i++] = nums[cur1++];
            }
        }
        while (cur1 <= mid) tmp[i++] = nums[cur1++];
        while (cur2 <= right) tmp[i++] = nums[cur2++];
        for (int j = left; j <= right; j++)
            nums[j] = tmp[j - left];
        return ret;
    }
};
class Solution {
public:
    vector<int> tmp;
    int reversePairs(vector<int>& nums) {
        tmp.resize(nums.size());
        return MergeSort(nums, 0, nums.size() - 1);
    }
    int MergeSort(vector<int>& nums, int left, int right)
    {
        if (left >= right) return 0;
        int mid = (right - left) / 2 + left;
        int ret = 0;
        ret += MergeSort(nums, left, mid);
        ret += MergeSort(nums, mid + 1, right);
        int cur1 = left, cur2 = mid + 1, i = 0;
        while (cur1 <= mid && cur2 <= right)
        {
            if (nums[cur1] <= nums[cur2])
            {
                tmp[i++] = nums[cur1++];
            }
            else
            {
                ret += mid - cur1 + 1;
                tmp[i++] = nums[cur2++];
            }
        }
        while (cur1 <= mid) tmp[i++] = nums[cur1++];
        while (cur2 <= right) tmp[i++] = nums[cur2++];
        for (int j = left; j <= right; j++)
            nums[j] = tmp[j - left];
        return ret;
    }
};